Coiled tubing optimized for long, horizontal completions

ABSTRACT

Coiled tubing optimized for long, horizontal completions is provided. The tubing comprises a body portion; at least two tapered portions, each tapered portion defining distal ends spaced apart from one another; and at least one bias weld portion. In some embodiments, the tapered portions are located between the body portion and the bias weld. The tubing has a weld thickness in the bias weld portion(s), a body thickness in the body portion, and a taper thickness in the tapered portions; generally, the thickness of the bias weld portion is greater than the body portion thickness. The wall thickness transitions from one end of each tapered portion to the other end of the same tapered portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application claims the benefit of prior U.S. ProvisionalApplication No. 61/538,276, filed Sep. 23, 2011.

FIELD OF THE INVENTION

The present invention relates generally to coiled tubing, and in aparticular though non-limiting embodiment, to methods and means ofincreasing the life of bias welds in coiled tubing.

BACKGROUND OF THE INVENTION

Coiled Tubing (CT) is frequently used in the completion of long,horizontal oil and gas wells. These wells have horizontal sectionsranging from about 2,000 to about 10,000 feet and they are increasingrapidly in length over time. The operating conditions require CT with anouter diameter (OD) of at least about 2.000 inches, wall thickness (WT)of at least about 0.156 inch, and steel tubing with a specified minimumyield strength (SMYS) of at least about 90,000 psi.

As those of skill in the relevant arts will readily appreciate, CT is aconsumable that is sold in discrete lengths known as “strings,” and eachCT string has a finite lifespan. The life of the CT string in longhorizontal wells is primarily governed by the durability of the helicalstrip joining weld known as the “bias weld.”

A typical CT string used in such wells will have between about 10 andabout 20 bias welds within it. Bias welds are the weakest point of theCT string and are modeled to have a life that is about 80% of the lifeof areas of the CT string without bias welds. The basis for modeling 80%life was determined in a 1995 joint industry study on plastic fatiguewhen CT strings were used only in vertical wells.

However, long, horizontal wells have operating conditions that createunique stresses on CT strings and bias welds in particular. Thesestresses, such as helical and sinusoidal buckling, are in addition tothe typical plastic strain CT strings encounter in vertical wells. Toimprove the economics of CT usage in long, horizontal wells it isimperative that the life of bias welds is increased.

The life of a bias weld is controlled by many variables, but WT has thelargest impact. For a typical string used in long, horizontal wells, a17% increase in WT leads to a 78% increase in bias weld life. As the WTincreases so does the overall weight of the CT string. The units thatcarry and deploy CT strings have structural and/or regulatory weightlimits.

To stay within weight limits, CT service companies must limit either WTor CT string length. Decreasing the CT string length reduces the marketpotential and profit margin for that CT string. For example, in theUnited States, a 15,000 foot CT string may only be utilized a third asmuch as a 19,000 foot CT string. Therefore, most service companiessacrifice bias weld life for longer CT strings.

There is, therefore, a long-standing yet unmet need for improved methodsand means of increasing the life of bias welds in coiled tubing used inlong, horizontal wells, which are still economical on a commercialscale.

SUMMARY OF THE INVENTION

In one example embodiment, a section of a coiled tubing is provided, thesection including a body portion having at least two tapered portions,with the tapered portions defining two distal ends spaced apart from oneanother, and each distal end having a wall thickness greater than anyother minimum wall thickness within the body portion. In otherembodiments, the section further includes at least one bias weldportion. In a further embodiment, the length of the section's bodyportion is longer than the length of the bias weld portion, and in astill further embodiment the section includes at least two bodyportions. In another embodiment, the section includes least two biasweld portions. In one example embodiment, a section's body portionthickness is about 0.190 inches, whereas in others the body portionthickness is either greater than or less than about 0.190 inches. Infurther embodiments, the body portion thickness transitions between afirst end of a tapered portion and a second end of a tapered portion. Instill further embodiments, the section has a bias weld thickness isabout 0.204 inches, whereas in others the section has a bias weldthickness of either greater than or less than about 0.204 inches. In apresently contemplated commercial embodiment, the section of coiledtubing is suitable for use as a section of a longer coiled tubingstring. In some embodiments, the length of the bias weld portion isabout 150 feet in length, whereas in others the length of the bias weldportion is either greater than or less than about 150 feet in length.

In another embodiment, a section of coiled tubing is provided, saidsection comprising a body portion having at least two tapered portions,the tapered portions defining two distal ends spaced apart from oneanother, wherein each distal end has a wall thickness greater than anyother minimum wall thickness within the body portion; and at least onebias weld portion, wherein the length of the body portion is longer thanthe length of the bias weld portion. In some embodiments, a minimum wallthickness located elsewhere within the body portion is about 0.175inches, while in other embodiments the minimum wall thickness is eithergreater than or less than about 0.175 inches. In further embodiments,the section includes at least two bias weld portions. In still furtherembodiments, the section of coiled tubing is suitable for use as asection of a longer coiled tubing string.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature, objects, and advantages ofthe present invention, reference should be made to the followingdrawings, wherein:

FIG. 1 is a cross-sectional view of a section of coiled tubing accordingto a first example embodiment of the invention.

FIG. 1A is a partial profile view of the example coiled tubing sectiondepicted in FIG. 1.

FIG. 2 is a cross-sectional view of a section of coiled tubing accordingto a second example embodiment of the invention.

FIG. 2A is a partial profile view of the example coiled tubing sectiondepicted in FIG. 2.

FIG. 3 is a cross-sectional view of a section of coiled tubing accordingto a third example embodiment of the invention.

FIG. 3A is a partial profile view of the example coiled tubing sectiondepicted in FIG. 3.

FIG. 4 is a cross-sectional view of a section of coiled tubing accordingto a fourth example embodiment of the invention.

FIG. 4A is a partial profile view of the example coiled tubing sectiondepicted in FIG. 4.

FIG. 5 is a cross-sectional view of a section of coiled tubing accordingto a fifth example embodiment of the invention.

FIG. 5A is a partial profile view of the example coiled tubing sectiondepicted in FIG. 5.

DETAILED DESCRIPTION OF SEVERAL EXAMPLE EMBODIMENTS

In one example embodiment of the invention, the improved coiled tubingincreases bias weld life while only slightly increasing overall weight.A presently preferred method of accomplishing this object is to employheavier WT tubing only at bias weld portions rather than throughout anentire length of the CT string.

In certain embodiments, the improved coiled tubing is made by usingsections of hot-rolled steel coils that have heavy WT at the bias welds,and lighter WT in the much longer body sections.

Turning now to FIG. 1, a cross-section of a section of a length ofcoiled tubing 100 is provided. The coiled tubing 100 has variable wallthickness. According to this embodiment, the lighter body portions 106of the tubing 100 have a constant wall thickness 107. Gradually, thewall thickness 108 increases, as shown in the taper portions 105. At thebias weld 103, and in the bias weld portion 104, the wall thickness 109is greater than the wall thickness 107 in the lighter body portions 106.FIG. 1 represents just one section of a larger coiled tubing string.According to further example embodiments, a completed coiled tubingstring comprises anywhere between about 20 and about 40 bias weldportions 104.

According to example embodiments, the bias weld portion 104 wallthickness 109 is about 0.204 inches, and the wall thickness 107 in thelighter body portions 106 is about 0.190 inches. However, other wallthicknesses 107 and 109 and outer diameters are contemplated. Forexample, in some embodiments the wall thickness is greater than about0.190 inches, whereas in other embodiments the wall thickness is lessthan about 0.190 inches. In a presently preferred embodiment, the bodythickness gradually transitions in thickness from one end of the taperportion to the other end of the taper portion.

In still further example embodiments, each bias weld portion 104 is 150feet in length, each taper portion 105 is about 150 feet in length, andeach lighter body portion 106 is about 1,200 feet in length. However,other portion lengths are contemplated and can easily be achieved withinthe scope of the invention. For example, in some embodiments the biasweld portion is greater than about 150 feet in length, while in otherembodiments the bias weld portion is less than about 150 feet in length.In still further embodiments, the body portion length is greater than orless than about 1,200 feet in length.

In other embodiments, the weld thickness is about 0.204 inches, thoughthis dimension is arbitrary and can be increased or decreased dependingupon the requirements of a given application. For example, in someembodiments the weld thickness is greater than about 0.204 inches,whereas in other embodiments the weld thickness is less than about 0.204inches.

According to one presently contemplated embodiment, an improved CTstring embodying the design shown in FIG. 1 has about a 78% increasedbias weld life with only about 1.2% more total weight. This added weightwould have only minimal impact on the CT string length. For example, ifa CT string length was previously limited to approximately 15,000 feet,example embodiments according the invention would only reduce the lengthby around 300 feet. For virtually all known CT service companies, thistrade-off would be readily accepted in order to achieve stronger,lighter strings of coiled tubing suitable for use in long, horizontalapplications while maintaining the integrity of associated bias welds.That said, total string lengths of greater than or less than about15,000 feet can be utilized while still achieving the advantages of thepresent invention.

FIGS. 2-5 and the profile views related thereto are cross-sectionalviews of non-limiting alternative embodiments of the disclosed coiledtubing sections, though those of ordinary skill in the art willappreciate that any number of alternative configurations can be achievedwithin the scope of the instant disclosure.

For example, in one alternative embodiment, a section of coiled tubinghaving at least two tapered portions is provided, wherein each distalend of said section has a wall thickness greater than any minimum wallthickness elsewhere within the section.

In one specific though non-limiting embodiment, at least one distal endof said section has a wall thickness of about 0.190 inches. In otherembodiments, however, said at least one distal end of said section has awall thickness of greater than about 0.190 inches. In still furtherembodiments, said at least one distal end of said section has a wallthickness of less than about 0.190 inches.

In another specific though non-limiting embodiment, at least one distalend of said section has a wall thickness of about 0.204 inches. In otherembodiments, however, said at least one distal end of said section has awall thickness of greater than about 0.204 inches. In still furtherembodiments, said at least one distal end of said section has a wallthickness of less than about 0.204 inches.

In yet another specific though non-limiting embodiment, a minimum wallthickness found elsewhere within the section is about 0.175 inches. Inother embodiments, however, said minimum wall thickness found elsewherewithin the section is greater than about 0.175 inches. In still otherembodiments, however, said minimum wall thickness found elsewhere withinthe section is greater than about 0.175 inches.

For still greater clarity, it will be appreciated that long sections(e.g., 1,500 feet to 3,500 feet or so) of coiled tubing may be formedand/or joined with other such sections, so that a resulting stringcomprises a plurality of conventional sections of coiled tubinginterspersed with, connected by, or terminated by one or more sectionsof the innovative tubing disclosed herein.

One distinguishing feature of the presently disclosed coiled tubingsections is that they comprise at least two tapered portions and have adistal wall thickness at the end of each section that is greater thanthe minimum wall thickness found anywhere else in the section. As FIGS.2-5 and their related profile views representatively show, an infinitevariety of potential taper geometries are possible, and tapered portionsmay be joined directly together or connected by body portions, etc. Thetapered portions may also be located at any point along the section,including the distal ends, adjoined within or in conjunction with a bodyportion, or on either side of a body portion, and/or any combinationthereof.

The foregoing specification is provided for illustrative purposes onlyand is not intended to describe all possible aspects of the presentinvention. Moreover, while the invention has been shown and described indetail with respect to several exemplary embodiments, those of ordinaryskill in the art will appreciate that minor changes to the description,and various other modifications, omissions and additions may also bemade without departing from the spirit or scope thereof.

The invention claimed is:
 1. A coiled tubing, comprising: a firstsection comprising a first body portion disposed between at least twofirst tapered portions, the first tapered portions defining two distalends spaced apart from one another, wherein each distal end has a wallthickness greater than a wall thickness of the first body portion, andwherein the first body portion, the two first tapered portions, and thetwo distal ends have substantially the same outer diameter; a secondsection comprising a second body portion disposed between at least twosecond tapered portions, the second tapered portions defining two distalends spaced apart from one another, wherein each distal end has a wallthickness greater than a wall thickness of the second body portion, andwherein the second body portion, the two second tapered portions, andthe two distal ends have substantially the same outer diameter; andwherein one distal end of the first section is welded to one distal endof the second section to form spoolable coiled tubing.
 2. The coiledtubing of claim 1, wherein the one distal end of the first section andthe one distal end of the second section that are welded to each othercomprise a bias weld portion.
 3. The a coiled tubing of claim 2, whereinthe length of the first and second body portions is longer than thelength of the bias weld portion.
 4. The coiled tubing of claim 2,wherein the bias weld portion has a thickness of about 0.204 inches. 5.The coiled tubing of claim 2, wherein the bias weld portion has athickness greater than about 0.204 inches.
 6. The coiled tubing of claim2, wherein the bias weld portion has a thickness less than about 0.204inches.
 7. The coiled tubing of claim 2, wherein a length of the biasweld portion is about 150 feet in length.
 8. The coiled tubing of claim2, wherein a length of the bias weld portion is greater than about 150feet in length.
 9. The coiled tubing of claim 2, wherein a length of thebias weld portion is less than about 150 feet in length.
 10. The coiledtubing of claim 1, wherein the first and second sections comprise atleast two bias weld portions.
 11. The coiled tubing of claim 1, whereinthe first and second body portions have a thickness of about 0.190inches.
 12. The coiled tubing of claim 1, wherein the first and secondbody portions have a thickness greater than about 0.190 inches.
 13. Thecoiled tubing of claim 1, wherein the first and second sections formpart of a longer spoolable coiled tubing string.
 14. The coiled tubingof claim 1, wherein the first and second body portions have a thicknessless than about 0.190 inches.
 15. The coiled tubing of claim 1, whereinthe first and second body portions have a thickness that transitionsbetween a first end of one of the first and second tapered portions anda second end of the other one of the first and second tapered portions,respectively.
 16. The coiled tubing of claim 1, wherein the first andsecond body portions include a constant wall thickness portion disposedbetween the at least two first and second tapered portions,respectively.
 17. A coiled tubing, comprising: a first sectioncomprising a first body portion disposed between at least two firsttapered portions, the first tapered portions defining two distal endsspaced apart from one another, wherein each distal end has a wallthickness greater than a wall thickness of the first body portion; andat least one first bias weld portion, wherein the length of the firstbody portion is longer than the length of the first bias weld portion,and wherein the first body portion, the two first tapered portions, thetwo distal ends, and the first bias weld portion have substantially thesame outer diameter; a second section comprising a second body portiondisposed between at least two second tapered portions, the secondtapered portions defining two distal ends spaced apart from one another,wherein each distal end has a wall thickness greater than a wallthickness of the second body portion; and at least one second bias weldportion, wherein the length of the second body portion is longer thanthe length of the second bias weld portion, and wherein the second bodyportion, the two second tapered portions, the two distal ends, and thesecond bias weld portion have substantially the same outer diameter; andwherein the first bias weld portion of the first section is welded tothe second bias weld portion of the second section to form spoolablecoiled tubing.
 18. The coiled tubing of claim 17, wherein a minimum wallthickness located within the first and second body portions is about0.175 inches.
 19. The coiled tubing of claim 17, wherein a minimum wallthickness located within the first and second body portions is greaterthan about 0.175 inches.
 20. The coiled tubing of claim 17, wherein aminimum wall thickness located within the first and second body portionsis less than about 0.175 inches.
 21. The coiled tubing of claim 17,wherein the first and second sections comprise at least two bias weldportions.
 22. The coiled tubing of claim 17, wherein the first andsecond sections form part of a longer spoolable coiled tubing string.23. The coiled tubing of claim 17, wherein the first and second bodyportions include a constant wall thickness portion disposed between theat least two first and second tapered portions, respectively.